User profile for user: doctorjay
doctorjay Author
User level: Level 1
8 points

Time Machine drive won't mount after power failures

My time machine drive will no longer mount. Over the weekend there were several brief (lights blinking off and back on) power failures that required rebooting the computer. the drive will no longer mount. I can see in disk utility the drive, container and time machine (greyed out). the message I get a message "The disk "Time Machine"can't be unlocked. A problem was detected with the disk that prevents it from being unlocked." Tried rebooting recovery mode, safe mode, command line to unlock . Anyone have any ideas short or reformatting and losing all the backups?


intel iMac with Sequoia, 12 tb toshiba drive.

iMac (2017 – 2020)

Posted on Jul 7, 2026 4:29 AM

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User profile for user: iamshivam
iamshivam
User level: Level 3
504 points

Posted on Jul 9, 2026 1:03 AM

The fact that the APFS volume is visible but fails specifically at the unlock stage after multiple power flickers points more toward APFS metadata or checkpoint corruption than a simple mount issue. I'd avoid running repair commands repeatedly because each write attempt can make recovery harder if the container is already damaged. Before doing anything destructive, create a sector-by-sector image of the entire 12 TB drive onto another disk if you have the space, then work on the clone.


If diskutil apfs list shows the volume but it won't unlock even with the correct password, check the system log (log stream --predicate 'process == "apfsd"') while attempting the mount. APFS usually reports whether it's failing on the encryption metadata, object map, or checkpoint validation, which tells you whether you're dealing with logical corruption or a failing drive. Since this happened immediately after repeated power interruptions, I'd also check the drive's SMART data, because I've seen marginal external HDDs expose APFS corruption only after an unclean shutdown.

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User profile for user: iamshivam
iamshivam
User level: Level 3
504 points

Jul 9, 2026 1:03 AM in response to doctorjay

The fact that the APFS volume is visible but fails specifically at the unlock stage after multiple power flickers points more toward APFS metadata or checkpoint corruption than a simple mount issue. I'd avoid running repair commands repeatedly because each write attempt can make recovery harder if the container is already damaged. Before doing anything destructive, create a sector-by-sector image of the entire 12 TB drive onto another disk if you have the space, then work on the clone.


If diskutil apfs list shows the volume but it won't unlock even with the correct password, check the system log (log stream --predicate 'process == "apfsd"') while attempting the mount. APFS usually reports whether it's failing on the encryption metadata, object map, or checkpoint validation, which tells you whether you're dealing with logical corruption or a failing drive. Since this happened immediately after repeated power interruptions, I'd also check the drive's SMART data, because I've seen marginal external HDDs expose APFS corruption only after an unclean shutdown.

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User profile for user: SpiderMac
SpiderMac
User level: Level 4
1,458 points

Jul 7, 2026 4:48 AM in response to doctorjay

Force Repair the APFS Container and Volume


Unplug your Time Machine drive, wait a few seconds, and plug it back in.

Open Terminal (found in Applications > Utilities, or via Recovery Mode).

Type the following command to identify the exact identifier of your drive:

diskutil list


Look for your external drive in the list. Note the identifier for the APFS Container (e.g., disk3 or disk4) and the specific Time Machine volume that is greyed out (e.g., disk3s1).

Run the repair command directly on the main Container (replace diskX with your correct drive number, e.g., disk3):

diskutil repairDisk /dev/diskX


If prompted to confirm, type y (yes) and press Enter.

Once that process finishes, run a deep repair on the APFS volume structure itself (replace diskXsY with your greyed-out volume identifier, e.g., disk3s1):

diskutil apfs repairVolume /dev/diskXsY


If Terminal successfully corrects the metadata inconsistency caused by the power surge, the volume will automatically unlock and mount normally, preserving all your historical backups.

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User profile for user: VikingOSX
VikingOSX
User level: Level 10
127,866 points

Jul 9, 2026 10:09 AM in response to doctorjay

The one consistent setting that I have is that no Mac will automatically try to power up after a power failure. The reason for this is to avoid the multiple interruptions that may occur to the boot process during initial power restoration. This is the bane of rotational drives, and may introduce corruption. I have moved on to SSD TM drives but still retain this Energy setting.


Settings > Energy : Start up when power is connected: [Never].


I always boot into Recovery mode before attempting to run Disk Utility First Aid on a Time Machine drive. That way, Spotlight or Time Machine itself are not attempting to use it.

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User profile for user: doctorjay
doctorjay Author
User level: Level 1
8 points

Jul 10, 2026 12:13 PM in response to iamshivam

thanks for the info. this is the system log stream using the above command. I have no idea what it means.

sudo log stream --predicate 'process == "apfsd"'                                                                                                                            








^[[3~^[[3~Timestamp                       Thread     Type        Activity             PID    TTL  


2026-07-10 02:01:41.218595-0400 0x2993d8   Default     0x0                  279    0    apfsd: (libxpc.dylib) [com.apple.xpc.activity:Client] _xpc_activity_dispatch: beginning dispatch, activity name com.apple.apfsd.obj_cache_stats_report, seqno 0


2026-07-10 02:01:41.218652-0400 0x2993d8   Default     0x0                  279    0    apfsd: (libxpc.dylib) [com.apple.xpc.activity:Client] _xpc_activity_dispatch: com.apple.apfsd.obj_cache_stats_report (0x7fe806705360): found an activity with matching seqno 0


2026-07-10 02:01:41.218711-0400 0x2993d8   Default     0x0                  279    0    apfsd: (libxpc.dylib) [com.apple.xpc.activity:Client] _xpc_activity_begin_running: com.apple.apfsd.obj_cache_stats_report (0x7fe806705360) seqno: 0.


2026-07-10 02:01:41.218763-0400 0x2993d8   Default     0x0                  279    0    apfsd: (libxpc.dylib) [com.apple.xpc.activity:Client] _xpc_activity_dispatch: lower half, activity name com.apple.apfsd.obj_cache_stats_report (0x7fe806705360), seqno from top half was 0


2026-07-10 02:01:41.218807-0400 0x2993d8   Default     0x0                  279    0    apfsd: (libxpc.dylib) [com.apple.xpc:connection] [0x7fe7f7f044e0] Channel returned listener port: 0x302f


2026-07-10 02:01:41.218826-0400 0x2993d8   Default     0x0                  279    0    apfsd: (libxpc.dylib) [com.apple.xpc.activity:Client] _xpc_activity_set_state: com.apple.apfsd.obj_cache_stats_report (0x7fe806705360), 2


2026-07-10 02:01:41.218841-0400 0x2993d8   Default     0x0                  279    0    apfsd: (libxpc.dylib) [com.apple.xpc.activity:Client] _xpc_activity_set_state: send new state to CTS: com.apple.apfsd.obj_cache_stats_report (0x7fe806705360), 2


2026-07-10 02:01:41.219048-0400 0x2993d8   Default     0x0                  279    0    apfsd: (libxpc.dylib) [com.apple.xpc.activity:Client] _xpc_activity_set_state_from_cts: com.apple.apfsd.obj_cache_stats_report (0x7fe806705360), set activity state to 2


2026-07-10 02:01:41.219106-0400 0x2993d8   Default     0x0                  279    0    apfsd: (libxpc.dylib) [com.apple.xpc.activity:Client] __XPC_ACTIVITY_CALLING_HANDLER__: com.apple.apfsd.obj_cache_stats_report (0x7fe806705360), current state 2, pending state 0


2026-07-10 02:01:41.219151-0400 0x2993d8   Default     0x0                  279    0    apfsd: (libxpc.dylib) [com.apple.xpc.activity:Client] _xpc_activity_set_state: com.apple.apfsd.obj_cache_stats_report (0x7fe806705360), 4


2026-07-10 02:01:41.219188-0400 0x2993d8   Default     0x0                  279    0    apfsd: (libxpc.dylib) [com.apple.xpc.activity:Client] __XPC_ACTIVITY_CALLING_HANDLER__ returned from handler: com.apple.apfsd.obj_cache_stats_report (0x7fe806705360), current state 2, pending state 4


2026-07-10 02:01:41.219221-0400 0x2993d8   Default     0x0                  279    0    apfsd: (libxpc.dylib) [com.apple.xpc.activity:Client] _xpc_activity_set_state: send new state to CTS: com.apple.apfsd.obj_cache_stats_report (0x7fe806705360), 4


2026-07-10 02:01:41.219925-0400 0x299468   Default     0x0                  279    0    apfsd: (libxpc.dylib) [com.apple.xpc.activity:Client] _xpc_activity_set_state: com.apple.apfsd.obj_cache_stats_report (0x7fe806705360), 5


2026-07-10 02:01:41.220198-0400 0x2993d8   Default     0x0                  279    0    apfsd: (libxpc.dylib) [com.apple.xpc.activity:Client] _xpc_activity_set_state: send new state to CTS: com.apple.apfsd.obj_cache_stats_report (0x7fe806705360), 5


2026-07-10 02:01:41.224491-0400 0x2993d8   Default     0x0                  279    0    apfsd: (libxpc.dylib) [com.apple.xpc.activity:Client] _xpc_activity_set_state_from_cts: com.apple.apfsd.obj_cache_stats_report (0x7fe806705360), set activity state to 1


2026-07-10 02:01:41.224553-0400 0x2993d8   Default     0x0                  279    0    apfsd: (libxpc.dylib) [com.apple.xpc.activity:Client] _xpc_activity_end_running: com.apple.apfsd.obj_cache_stats_report (0x7fe806705360) seqno: 0.


Does this help ?

none of the unlock, force repair or repair volume works.


I do have a carbon copy cloner backup also.


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Time Machine drive won't mount after power failures

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